Measurement of the mechanics of respiration in unanesthetized guinea pigs is used as a bioassay method for the assessment of irritant potency. During the past year we completed studies on the effects of mineral oil and motor oil on the response to sulfur dioxide. We have found that sulfite complexes are present on samples of the aerosols of iron and copper which potentiated the response to sulfur dioxide. (These analyses were performed at Brigham Young University). During the coming year we plan to generate aerosols of iron-sulfite and copper-sulfite complexes and test their irritant potency. We also plan to expose animals to mixtures of formaldehyde and sulfur dioxide. Our rationale for this is that sulfur-aldehyde complexes have been found in the atmosphere. Past studies have provided us with basic data on the two compounds alone.